Method and apparatus for heat treating material

ABSTRACT

A method and apparatus for quenching a material. The apparatus includes a support for receiving the material; and an outlet adjacent the support for impinging a fluid against a first section of the material. The apparatus increases a cooling rate of the first section relative to a cooling rate of a second section of the material, preferably minimizing a differential between the cooling rate of the first section and the cooling rate of the second section.

BACKGROUND OF INVENTION

[0001] This invention relates to a method and an apparatus for heattreating a material. Specifically, the present invention relates to amethod and apparatus for fluid impingement quenching a forging.

[0002] Conventional quenching techniques include bath quenching and fanquenching.

[0003] The bath quenching process immerses a forging within a containerof oil. The oil acts as a heat sink to cool the forging. The processtypically agitates the oil to increase the rate of heat transfer.

[0004] The oil bath quenching process has numerous drawbacks. The firstdrawback relates to the handling of the oil. Oil handling must followspecific procedures for environmental and safety concerns.

[0005] The second drawback relates to the waste stream. The used oilmust enter the waste stream properly. Environmental and safety concernsdemand the proper entry of the used oil into the waste stream.

[0006] The third drawback relates to predictability. Oil bath quenchingis not a fully controllable process. For instance, the oil bathquenching process lacks the ability to control local heat transfer ratesprecisely. Generally speaking, oil bath quenching produces an arbitraryheat transfer coefficient of between approximately 70 and 140 BTU/hr ft²° F. uniformly across the forging.

[0007] The final drawback relates to residual stress. Oil bath quenchingtends to produce high residual stress values due to the arbitrary heattransfer coefficient. Such values can produce cracking and distortion ofthe forging.

[0008] The second conventional quenching technique is fan quenching. Thefan quenching process uses forced convection to cool a forging. One ormore fans propel air against the forging to increase the rate of heattransfer. While avoiding the environmental issues encountered with oilbath quenching, the fan quenching process does have several drawbacks.Notably, the fan quenching process may not create the heat transferrates needed to produce the desired material properties in hightemperature aerospace alloy forgings. Second, the fan quenching processalso lacks the ability to control the heat transfer rates locally atvarious locations on the forging.

[0009] New high temperature aerospace alloys have placed greater demandson the quenching process. These new alloys require a high lower limit ofthe cooling rate during quenching to achieve metallurgical requirements(e.g. tensile strength). As a result, fan quenching is no longer anoption for these new high temperature aerospace alloys.

[0010] These new high temperature aerospace alloys also demand that thequenching process control the upper limit of the cooling rate so as toavoid the formation of cracks in the forging. As a result, oil bathquenching is no longer an option for these new high temperatureaerospace alloys.

[0011] In other words, the quenching process must remain within alimited range of cooling rate values to produce the desired materialqualities in the forging. Unfortunately, conventional quenchingtechniques do not appear to achieve these goals satisfactorily forcertain applications, such as these new high temperature aerospacealloys.

SUMMARY OF INVENTION

[0012] It is an object of the present invention to provide an improvedquenching method and apparatus.

[0013] It is a further object of the present invention to provide aquenching technique that reduces environmental concerns.

[0014] It is a further object of the present invention to provide aquenching technique that produces less scrap during quenching caused bycracking and distortion.

[0015] It is a further object of the present invention to provide aquenching technique that produces less scrap during subsequentmanufacturing operations caused by residual stress effects.

[0016] It is a further object of the present invention to provide aquenching technique that consumes less raw material.

[0017] It is a further object of the present invention to provide aquenching technique that is controllable.

[0018] It is a further object of the present invention to provide aquenching technique that can keep cooling rate values within a limitedrange.

[0019] These and other objects of the present invention are achieved inone aspect by a method of quenching a material, comprising the steps of:providing a material having a first section and a second section; andpropelling a fluid against the first section to increase the coolingrate of the first section relative to a cooling rate of the secondsection.

[0020] These and other objects of the present invention are achieved inanother aspect by a method of adjusting the cooling rate of a forgingduring quenching, comprising the steps of: providing a forging having afirst section with a first cooling rate and a second section having asecond cooling rate; and propelling a fluid against the first section inorder to minimize a differential between the first cooling rate and thesecond cooling rate.

[0021] These and other objects of the present invention are achieved inanother aspect by an apparatus for quenching a material, comprising: asupport for receiving the material; and an outlet adjacent the supportfor impinging a fluid against a first section of the material, so that acooling rate of the first section increases relative to a cooling rateof a second section of the material.

BRIEF DESCRIPTION OF DRAWINGS

[0022] Other uses and advantages of the present invention will becomeapparent to those skilled in the art upon reference to the specificationand the drawings, in which:

[0023]FIG. 1 is an exploded, perspective view of one embodiment of thequenching apparatus of the present invention;

[0024]FIG. 2 is a cross-sectional view of the quenching apparatus takenalong line 11-11 in FIG. 1;

[0025]FIG. 3 is a plan view of one component of the quenching apparatusshown in FIG. 1;

[0026]FIG. 4 is a detailed view of a portion of the component shown inFIG. 3;

[0027]FIG. 5 is a cross-sectional view of the component taken along lineV-V in FIG. 4;

[0028]FIG. 6 is an elevational view of a second component of thequenching apparatus shown in FIG. 1; and

[0029]FIG. 7 is an elevational view of a section of the quenchingapparatus shown in FIG. 1 with a forging placed therein.

DETAILED DESCRIPTION

[0030]FIG. 1 displays an exploded perspective view of one embodiment ofa quenching apparatus 100. The quenching apparatus 100 can receive anannular forging F (only partially shown in the figure), such as aturbine disk or an air seal. Although accommodating an annular shape,the apparatus could heat treat any shape of forging F.

[0031] Similarly, the apparatus 100 could quench a forging made from anymaterial. The preferred material, however, is a high temperatureaerospace alloy. Generally speaking, such material must have adequateperformance characteristics, such as tensile strength, creep resistance,oxidation resistance, and corrosion resistance, at high temperatures.Course grained nickel alloys are especially prone to quench cracking dueto a ductility trough at the upper temperatures (e.g. 1800-2100° F.) ofthe quenching process. Examples of high temperature aerospace materialsinclude nickel alloys such as IN100, IN1100, IN718, Waspaloy and IN625.

[0032] To achieve these characteristics, the aforementioned alloysdemand precise control of the quenching process. Precise control isnecessary to avoid cracking of the forging during quenching and to avoidresidual stress effects during subsequent manufacturing operations onthe forging. Typically, most forgings that exhibit cracks duringquenching are considered scrap.

[0033] The quenching apparatus 100 preferably can provide impingementcooling to all surfaces of the forging F. The apparatus 100 includes afirst cooling section 101, a second cooling section 103 and a centralcooling section 105. Each section will now be described in furtherdetail.

[0034]FIG. 3 displays the first cooling section 101. The first coolingsection 101 preferably corresponds to a bottom of the forging F. Thefirst cooling section 101 includes one or more supports 107 arrangedaround the apparatus 100. Although the figure displays three, thepresent invention could use any suitable number of supports 107.

[0035] The supports 107 have recesses in which a plurality of concentricpipes 109 can reside. Although the figures show five, the presentinvention could utilize any number of pipes 109. The number of pipes 109depends upon the geometry of the forging F. A larger forging F requiresmore pipes 109.

[0036] A plurality of spacers 111 secure to the supports 107 withconventional fasteners. The spacers 111 serve to retain the pipes 109 tothe supports 107. Although the figures show each spacer 111 retainingmultiple pipes 109, the spacer 111 could retain only one pipe. Thiswould allow the individual adjustment of pipes 109 without disturbingthe other pipes 109. Another important function of the spacers will bediscussed below.

[0037] As seen in FIG. 2, the top of the forging F could have adifferent shape than the bottom of the forging F. Accordingly, thesecond cooling section 103 may not mirror the shape of the first coolingsection 101. Rather, the second cooling section 103 preferably conformsto the top of the forging F.

[0038] Similar to the first cooling section 101, the second coolingsection 103 includes one or more supports 115, concentric pipes 117 andspacers 119. When fastened to the supports 115, the spacers 119 securethe pipes 117 to the supports 115. The supports 107,115 and the spacers111,119 could be made from any material suitable to the demands of thequenching process.

[0039] For versatility, the apparatus 100 should accommodates forgings Fof various shapes. For every forging F, the cooling sections 101, 103should generally conform to the specific shape. This could beaccomplished with conventional techniques. For example, the apparatuscould utilize supports 107, 115 specific to each forging shape.

[0040] Alternatively, the same supports 107, 115 could be used for everyforging F. To accommodate different shapes, the universal supportsshould include features (not shown) to allow selective positioning ofeach of the pipes 109, 117. In one possible arrangement, the universalsupports could have height adjustable platforms upon which the pipes109, 117 rest. The platforms could use a threaded shaft to adjustheight.

[0041] In addition, either of the supports 107, 115 could be sized andshaped to allow an outermost pipe 109,117 to surround the outer diameterof the forging F. This arrangement allows the apparatus 100 to quenchthe outer diameter of the forging F. Not all forgings F, however,require quenching at the outer diameter. As an example, forgings F withthin sections at the outer diameter typically do not require quenching.

[0042]FIGS. 4 and 5 display one of the pipes 109. The pipe 109 isannular to provide axisymmetric cooling to the annular forging F. Thetubes 113 can be made from any suitable material, such as tooling steel(e.g. AMS5042, AMS5062, AIS14340), stainless steel (AISI310, AISI316,17-4HP), copper and brass. As an example, the pipes 109 could have aninner diameter of between approximately 0.7″ and 1.3″ and have asuitable thickness. The specific values will depend upon the demands ofthe quenching process.

[0043] The pipes 109,117 each have an inlet (not shown) attached to afluid source 127 using conventional techniques. The source 127 could useconventional valves (not shown) to control fluid flow to each pipe109,117. The valves could either be manually or computer-controlled. Thebenefits of having such control will become clear below.

[0044] The pipes 109,117 have an arrangement of openings 131 therein.Preferably, the openings are regularly arranged around the pipes 109,117to provide axisymmetric cooling to the forging F. However, non-symmetricarrangements are possible. As seen in FIG. 5, The openings 131 span anangle α of between approximately 25° and 270° of the circumference ofthe pipe 109,117. Preferably, the angle α is approximately 90°.

[0045] The openings 131 in the pipes 109,117 define outlet nozzles forthe fluid to exit the cooling sections 101,103. The fluid propels fromthe openings 131 to cool the forging F. The openings 131 could haveeither sharp edges or smooth edges in order to provide a desired nozzleconfiguration. Specific geometric aspects of the openings 131 will bediscussed in detail below.

[0046]FIG. 6 displays the central cooling section 105. The centralcooling section 105 preferably resides within the inner bore of theforging F. As with the outer diameter, the inner diameter of the forgingF may not require quenching. Forgings F with thin sections at the innerdiameter typically do not require quenching.

[0047] Similar to the pipes 109,117, the central cooling section 105 isa pipe that includes an inlet 133 attached to the fluid source 127 usingconventional techniques. The central cooling section 105 also includes aplurality of openings 135 at an outlet end. The size and shape of thecentral cooling section 105 depends upon the geometry of the forging F.

[0048] Assembly of the apparatus 100 proceeds as follows. The assembledfirst cooling section 101 receives the forging F. Specifically, theforging F rests on the spacers 111.

[0049] Then, the second cooling section 103 is placed over the forgingF. Likewise, the spacers 111 rest on the forging F. Next, the centralcooling section 105 is placed inside the central bore of the annularforging F. The central cooling section 105 preferably rests on thesupports 107 of the first cooling section 101, and is spaced from theforging F by abutting the distal ends of the spacers 111. Otherarrangements, however, are possible. The apparatus 100 is now ready tobegin the quenching operation. The apparatus could utilize any suitablefluid, such as a gas, to quench the F. Preferably, the present inventionuses air. The source 127 could have a diameter of between approximately2.5″ and 3.5″. The source 127 could also supply approximately 12 lb/secof ambient (e.g. 65-95° F.) air to the apparatus 100 at a pressure ofbetween approximately 45 and 75 psig. Again, the specific values willdepend upon the demands of the quenching process.

[0050] Generally speaking, one goal of the present invention is tocontrol the cooling rate of the forging F precisely. This precisecontrol allows the use of impingement cooling on the forging F.Impingement cooling is a subset of forced convection cooling thatproduces significantly higher heat transfer coefficients than theremainder of the forced convection regime. For example, conventionalforced air convection can achieve heat transfer coefficients ofapproximately 50 BTU/hr ft² ° F. with typical equipment. Impingementcooling, on the other hand, can achieve heat transfer coefficients up toapproximately 300 BTU/hr ft² ° F.

[0051]FIG. 7 provides the spatial relationship between the pipes 109,117and the forging F. Although displaying the first and second coolingsections 101,103, the spatial relationships shown in this figure arealso applicable to the central cooling section 105. As seen in thefigure, the spacers 111 provide a gap between the forging F and thepipes 109,117.

[0052] The openings 131 in the pipe preferably have a diameter dadequate to propel a sufficient amount of fluid against the forging F toperform the quenching process. As an example, the diameter d of theopenings 131 could be between approximately 0.55″ and 0.75″. At thisdiameter d, preferably between approximately 0.002 lb/sec and 0.01lb/sec of fluid flows through each opening 131 at a velocity of betweenapproximately 200 ft/sec and 1000 ft/sec.

[0053] The gaps formed between the pipes 109,117 and the forging Fcreated by the spacers 111 are an essential aspect of the presentinvention. The spacers 111 define a distance Z between the pipes 109,117and the forging F. The distance to diameter ratio (Z/d) should rangebetween approximately 1.0 and 6.0.

[0054] A circumferential spacing X exists between adjacent openings 131in the pipes 109,117. The circumferential spacing of the openings 131ensures adequate fluid flow to the forging F to achieve the desiredcooling rate. The circumferential arrangement of the apertures 131 alsoensures axisymmetric cooling of the forging F. The circumferentialspacing to diameter ratio (X/d) should be between approximately 0.0 and24.0.

[0055] Finally, a radial spacing Y exists between adjacent openings 131in the pipes 109. Similarly, the radial spacing of the openings 131ensures adequate fluid flow to the forging F to achieve the desiredcooling rate. The radial spacing to diameter ratio (Y/d) should bebetween approximately 0.0 and 26.0.

[0056] Using these parameters, the present invention can treat allsections of the forging using impingement cooling. Impingement coolingis preferred because of the combined effect of increased turbulence andincreased jet arrival velocity significantly increases the heat transfercoefficient of the apparatus 100.

[0057] By varying the aforementioned parameters within the suitableranges, the present invention can achieve another goal of the presentinvention—to reduce any differential between the cooling rates ofdifferent areas of the forging F. Ideally, the present invention seeksto equalize the cooling rates across all areas of the forging.

[0058] The present invention reduces temperature gradients within theforging F by providing more impingement cooling to one area of theforging F compared to another area of the forging F. In terms of heattransfer, the volume of an object equates to thermal mass and thesurface area of the object equates to cooling capacity. Objectsexhibiting a low surface area to volume ratio cannot transfer heat asreadily as objects with higher surface area to volume ratios.

[0059] The present invention seeks to increase the heat transfer ofareas of the forging F that exhibit low surface area to volume ratios.Practically speaking, the present invention provides more cooling tosurfaces of the forging F located adjacent larger volumetric sectionsthan surfaces of the forging F located adjacent smaller volumetricsections.

[0060] The present invention can locally adjust impingement cooling byvarying any of the aforementioned characteristics. For example, one canselectively adjust cooling to desired areas of the forging F byadjusting the diameters of the pipes 109,117, by adjusting the diameterof the openings 131, by adjusting the size of the spacer 111 or byadjusting the density of the openings 131 (ie. adjust spacing distancesX or Y) during the system design stage. During operation of theapparatus 100, one can selectively adjust the cooling to desired areasof the forging F by adjusting pressure in each pipe 109,111,133. Theaforementioned valves on the supply 127 could be used to adjustpressure. Any other technique to adjust pressure could also be used.

[0061] The present invention could leave these characteristics staticduring the quenching process. In other words, the apparatus 100 couldkeep the selected pressures in the pipes 109,111,133 constant throughoutthe entire temperature range of the quenching process. Alternatively,the present invention could dynamically adjust the pressures in thepipes 109,111,133 during the quenching process. For example, theapparatus 100 could operate at a desired pressure until the course grainnickel alloy forging F exits the temperature range of the ductilitytrough (e.g. 1800-2100° F.). Thereafter, the apparatus could operate ata reduced pressure for the remainder of the quenching process. Othervariations are also possible.

[0062] The present invention can produce heat transfer coefficientsgreater than those created by oil bath quenching (e.g. 70-140 BTU/hr ft²° F.) or fan quenching (e.g. 50 BTU/hr ft² ° F.). The present inventioncan produce a heat transfer coefficient of approximately 300 BTU/hr ft²° F.

[0063] Despite the higher heat transfer coefficient, the quenchedproducts that the present invention produces exhibit lower residualstress values than those products created by oil bath quenching. Thearbitrary cooling rate of oil bath quenching produces high residualstress values. The present invention, on the other hand, achieves lowerresidual stress values because of the ability to differentially cool theforging F (i.e. control the temperature gradients across the forging).Note that reference to the residual stress values produced by fanquenching is not appropriate because fan quenching cannot meet thecooling requirements needed to quench high temperature aerospace alloys.

[0064] The present invention has been described in connection with thepreferred embodiments of the various figures. It is to be understoodthat other similar embodiments may be used or modifications andadditions may be made to the described embodiment for performing thesame function of the present invention without deviating therefrom.Therefore, the present invention should not be limited to any singleembodiment, but rather construed in breadth and scope in accordance withthe recitation of the appended claims.

1. A method of quenching a material, comprising the steps of: providinga material having a first section and a second section; and propelling afluid against said first section to increase a cooling rate of saidfirst section relative to a cooling rate of said second section.
 2. Themethod as recited in claim 1, wherein said fluid comprises a gas.
 3. Themethod as recited in claim 1, wherein said propelling step generallyminimizes a gradient between a temperature of said first section and atemperature of said second section.
 4. The method as recited in claim 1,wherein the propelling step comprises impinging said fluid against saidfirst section to provide impingement cooling at said first section. 5.The method as recited in claim 1, wherein the propelling step remainsconstant during quenching.
 6. The method as recited in claim 1, whereinthe propelling step varies during quenching.
 7. The method as recited inclaim 6, wherein the propelling step varies by adjusting a pressure ofsaid fluid.
 8. A method of adjusting the cooling rate of a forgingduring quenching, comprising the steps of: providing a forging having afirst section with a first cooling rate and a second section having asecond cooling rate; and propelling a fluid against said first sectionin order to minimize a differential between said first cooling rate andsaid second cooling rate.
 9. The method as recited in claim 8, whereinsaid fluid is a gas.
 10. The method as recited in claim 8, wherein saidpropelling step generally minimizes a gradient between a temperature ofsaid first section and a temperature of said second section.
 11. Themethod as recited in claim 8, wherein the propelling step comprisesimpinging said fluid against said first section to provide impingementcooling at said first section.
 12. The method as recited in claim 8,wherein the propelling step remains constant during quenching.
 13. Themethod as recited in claim 8, wherein the propelling step varies duringquenching.
 14. The method as recited in claim 13, wherein the propellingstep varies by adjusting a pressure of said fluid.
 15. An apparatus forquenching a material, the material having a first section and a secondsection, said apparatus comprising: a support for receiving thematerial; and an outlet adjacent said support for impinging a fluidagainst the first section of the material, so that a cooling rate of thefirst section increases relative to a cooling rate of the secondsection.
 16. The apparatus as recited in claim 15, wherein said outlethas a diameter (d) and is positioned a distance (Z) from the materialplaced in said support, and Z/d is between approximately 1.0 and 6.0.17. The apparatus as recited in claim 15, wherein said outlet comprisesa plurality of outlets each having a diameter (d), adjacent outletshaving a spacing (s) therebetween, and s/d is less than approximately26.0.
 18. The apparatus as recited in claim 17, wherein said spacing isa circumferential spacing (X) and X/d is less than approximately 26.0.19. The apparatus as recited in claim 17, wherein said spacing is aradial spacing (Y) and Y/d is less than approximately 24.0.
 20. Theapparatus as recited in claim 15, wherein said outlet comprises aplurality of outlets in an annular pipe.